board: qcs404-evb: drop board code

board: qcs404-evb: drop board code

This board is entirely supported by the generic arch code and DTS. The
board code used to handle turning on the vbus regulator, however this is
now handled via DT.

With this, the board specific defconfig is also no longer needed, so
drop it as well.

Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Reviewed-by: Sumit Garg <sumit.garg@linaro.org>
Tested-by: Sumit Garg <sumit.garg@linaro.org> #qcs404
Signed-off-by: Caleb Connolly <caleb.connolly@linaro.org>